Filtering apparatus

ABSTRACT

A liquid filtering apparatus for mounting in a housing defining an inlet and a drain. The liquid filtering apparatus is positioned in use to filter liquid flowing from the inlet ( 23 ) to the drain. The apparatus comprises a permeable screen ( 19 ) rotatable about a substantially horizontal axis and forming a barrier between the inlet and the drain. A rotatable wheel is disposed within the screen and coupled to the screen so that rotation of the wheel causes rotation of the screen. The wheel is defined by vanes ( 5 - 12 ) extending towards the screen so as to divide a space around which the screen is arranged into sections which are substantially isolated from each other except via the drain. A stationary baffle ( 13 ) is arranged adjacent a portion of the screen to prevent liquid from flowing into the wheel through that portion of the screen. The baffle is positioned such that water flows more readily into sections of the wheel on one side of a vertical plane through the rotation axis than the other sections. Thus the wheel is unbalanced by water retained in sections of the wheel so as to cause the wheel to rotate.

[0001] The present invention relates to a liquid filtering apparatus,and in particular to such an apparatus which is capable of filtering aliquid such as water to remove solids.

[0002] Rotating drum screens are known for removing solid waste materialfrom flows of, for example, water. Such screens are generally used forremoving floating debris such as leaves or small pieces of wood fromriver water at the intake to industrial plant, although some rotatingscreens have been installed in fish farms to prevent small fish beinglost at the overflow of ponds. In a rotating drum screen, a perforatedcylindrical drum is supported in a channel so as to rotate about ahorizontal axis, the drum being partially submerged in water flowingthrough the channel. Water enters the interior of the perforated drumand exits from one end of the drum through a simple circular opening ina sidewall of the channel in which the drum is supported. The drum isarranged such that the water flow causes the drum to rotate.

[0003] The rotation of the drum causes any solid matter in the mainwatercourse which becomes temporarily attached to the outside surface ofthe drum to be washed off. In one known arrangement, the flow of waterbeneath the drum assists in causing its rotation in a manner equivalentto a conventional undershot water wheel but further torque is applied tothe drum as a result of the positioning of an impeller in the end of thedrum from which water issues and the provision of helical vanes on theinterior of the drum. Water entering the drum flows axially towards oneend of the drum and in so doing interacts with the vanes and impeller tocause the drum to rotate.

[0004] The known rotating drum screens are particularly advantageous inthat they do not require an external power source. The screen does notblind, and there is no need for regular maintenance. As a result theknown rotating drum screens have proved successful in circumstanceswhere there is a continuous relatively high volume flow of relativelyclean water.

[0005] One of the problems confronted by the water industry is that ofhandling storm water overflows from sewerage systems. In somecircumstances, in the event of very heavy rain, surface water enterssewerage systems and mixes with the wastewater being transported to atreatment plant. The combined flow of wastewater and rainwater can begreater than the maximum flow which can be carried by the seweragesystem. To accommodate such temporary conditions, it is conventionalpractice to provide overflow chambers in sewerage systems to temporarilystore excess flows. Unfortunately, unless such chambers are very largeindeed, in exceptional weather conditions raw sewage can overflow fromsuch chambers into, for example, surface waterways. In circumstanceswhere overflows are likely to occur, for example in periods ofexceptionally heavy rain, it is usually arranged that any wastewaterwhich does escape from a sewerage system will be very rapidly dilutedand therefore not lead to major problems. It is not acceptable, however,if any overflow from a sewerage system results in solid materialsreaching surface watercourses.

[0006] In addressing the above problem, and also the problem of findingan efficient mechanism for dealing with primary separation of liquidfrom solids in sewage treatment works, the possibility of using aconventional rotating drum screen was considered. It was found, however,that the conventional rotating drum screens were not adequate becausewhen the screens are only rotated on fairly rare occasions, for examplein the event of flooding, the relatively low torque generated by axialflow along the vanes within the drum was insufficient to reliably startthe rotation of the drum. Furthermore, given the nature of the solidmaterial included in flows of sewage it was difficult to avoid thescreens becoming clogged with solid material without providing someadditional cleaning of the screen surface and this required more powerthan that which was available from the conventional rotating drum screenassembly.

[0007] This problem has been addressed in published patent specificationno. WO-A-96/27422 wherein a permeable screen defining a cylindrical bodypartly submerged in the liquid to be filtered is described. Theapparatus is driven by the weight of water disposed within chambers ofthe body. Inlet water is filtered into a higher level chamber with alower chamber being drained by a side-drain. Thus the weight of water inthe higher level chamber provides the driving torque. However, it wasfound, as a result of the relationship between the liquid inlet anddrain from the cylindrical body, that the apparatus could only process asmall amount of water and at low water flow did not function at all.

[0008] It is an object of the present invention to obviate or mitigatethe problems outlined above.

[0009] According to the present invention, there is provided a liquidfiltering apparatus for mounting in a housing defining an inlet and adrain, the liquid filtering apparatus being positioned in use to filterliquid flowing from the inlet to the drain, the apparatus comprising apermeable screen rotatable about a substantially horizontal axis andforming a barrier between the inlet and the drain, a rotatable wheeldisposed within the screen and coupled to the screen so that rotation ofthe wheel causes rotation of the screen, the wheel defining vanesextending towards the screen to divide a space around which the screenis arranged into sections which are substantially isolated from eachother except via the drain, and a stationary baffle arranged adjacent aportion of the screen to prevent liquid from flowing into the wheelthrough that portion of the screen, the baffle being positioned suchthat water flows more readily into sections of the wheel on one side ofa vertical plane through the rotation axis than the other sections,whereby the wheel is unbalanced by water retained in sections of thewheel so as to cause the wheel to rotate.

[0010] Thus, the rotatable screen is rotated by a force generated by theweight of liquid in one or more sections of the wheel, the water beingretained by the wheel so as to maximise the applied torque.

[0011] It has been found that an apparatus in accordance with thepresent invention is able to rotate quickly and reliably even atrelatively low water flow rates. These characteristics mean that anapparatus in accordance with the invention is not only more efficient atlow water flow but is also able to process a larger amount of water thanin prior art arrangements.

[0012] The apparatus may include a plate formed so as to obstructcommunication between the drain and upper sections of the wheel intowhich water can flow readily.

[0013] The baffle may be disposed between the screen and wheel. Thebaffle may extend around a lower portion and one side of the wheel. Thebaffle may extend around more than 180° relative to the rotational axis,one edge of the baffle being located above the rotation axis and theother edge being located to one side of the rotation axis. The bafflemay extend from a point vertically above the axis to a pointhorizontally spaced from the axis.

[0014] The vanes may extend radially from a shaft, which defines therotational axis of the wheel. Alternatively the vanes may be swept backrelative to the direction of the rotation of the wheel. The shaft mayextend between bearings mounted on opposite walls of a chamber.

[0015] Drains are may be formed in one or both walls of the chamber.

[0016] The apparatus of the invention may be mounted in the manner of acantilever from one wall of a chamber.

[0017] Embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings, in which:

[0018]FIG. 1 is a schematic horizontal cross-sectional view of a firstembodiment of the present invention;

[0019]FIG. 2 is a view on the lines 2-2 of FIG. 1, the cross-sectionalview of FIG. 1 being taken on the lines 1-1 of FIG. 2;

[0020]FIG. 3 is an end perspective view of components of the embodimentshown in FIG. 1;

[0021]FIGS. 4, 5, 6 and 7 are end views of components of the embodimentof FIG. 1 illustrating the operation of the embodiment;

[0022]FIG. 8 is a schematic cross-sectional view similar to that of FIG.1 but of a second embodiment of the present invention; and

[0023]FIG. 9 illustrates a sealing arrangement which may be provided atone end of the embodiment of FIG. 1.

[0024] Referring to FIGS. 1 to 3, the illustrated embodiment comprises ashaft 1 journalled in bearings 2 which are mounted in concrete walls 3and 4. The shaft 1 supports eight planar vanes 5, 6, 7, 8, 9, 10, 11 and12 which rotate with the shaft 1.

[0025] A baffle 13 extends through 270° around the rotation axis of theshaft 1. The end of the baffle 13 adjacent the wall 3 is closed by acircular plate which is supported by but does not rotate with the shaft1. The other end of the baffle is supported on a plate 14 in which anaperture is formed which is of the same shape and is in register with acircular aperture formed in the wall 4. As shown in FIG. 2, thatcircular aperture has an edge 15 which extends through 360° around theaxis of the shaft 1. An extension 16 of the plate 14 (which preferablycomprises stainless steel) forms a barrier within the edge 15 extending90° around the shaft 1 from a point on edge 15 vertically above theshaft 1 to a point on edge 15 horizontally spaced from the shaft 1. Thebarrier 16 has inner edges 17 a (vertically extending) and 17 b(horizontally extending). The inner edges 17 a and 17 b are connected bya further edge 18 which extends around a portion of the barrier 16 whichprovides support for the bearing 2. It will be appreciated that analternative means of support for bearing 2 could be provided.

[0026] A cylindrical screen 19 extends from a circular end plate 20which is mounted on the shaft 1 so as to rotate with the shaft. Theother end of the screen 19 is mounted by means not shown to enable thescreen to rotate relative to the plate 14.

[0027] The vanes 5 to 12 extend towards the screen 19. (In FIG. 3 partof the screen 19 is shown in broken lines to indicate the periphery ofthe screen 19 so that the vanes may be seen more clearly. The barrier 16is also omitted from FIG. 3 for clarity). The radially outer edges ofthe vanes extend to adjacent the radially inner surface of the baffle 13such that a space around which the screen 19 extends is divided intoeight sections which are substantially isolated from each other exceptat the end of the assembly adjacent the wall 4. Thus the shaft 1, thevanes supported by the shaft and the screen 19 define a wheel rotatableas a single unit, the baffle 13 being interposed between the radiallyouter edges of the vanes and the screen 19.

[0028] The opening defined by edges 15,17 a, 17 b and 18 shown in FIG. 2represents a drain through which water retained by the wheel on eitherside of the vanes 8, 9, 10, 11 and 12 can flow to, for example, a watercourse. Any section of the wheel defined between two vanes which areboth located at positions between the edges 17 a and 17 b of FIG. 2 willbe retained in that section by the barrier 16 unless the wheel rotatesuntil at least one of the vanes has passed the edge 17 b.

[0029] Referring to FIGS. 4 to 7, these Figures illustrate the operationof the device illustrated in FIGS. 1 to 3. The assembly is mountedbetween two end walls 21 and 22 which extend between the sidewalls 3 and4 of FIG. 1. The chamber defined by the four walls 3, 4, 21 and 22extends upwards from a channel having an inlet 23 and an outlet 24. Innormal conditions, contaminated water such as sewage enters the chamberthrough inlet 23 and exits through outlet 24, the upper surface of thewater being represented by line 25. The screen 19 is located at asufficient height such that in normal conditions it is well above thewater surface 25. This is represented in FIG. 4.

[0030] In storm conditions, for example after periods of very heavyrain, the water flow through the inlet 23 may be greater than thecapacity of the outlet 24 to discharge the inflow of water from thechamber. In such circumstances the water level 25 may rise to theposition indicated in FIGS. 5, 6 and 7 by line 26. Water flows throughall portions of the screen 19 immersed below the level 26 but can onlyenter the wheel sections between vanes 5 and 6 and between vanes 6 and 7because of the presence of the baffle 13. Some minor leakage of watermay occur into the remaining sections of the wheel but such water willbe rapidly discharged through the opening shown in FIG. 2. As a result,the wheel is unbalanced and the weight of water retained between vanes5, 6 and 7 applies a torque to the wheel in the direction indicated byarrow 27. This causes the wheel to rotate from the position shown inFIG. 5 towards the position shown in FIG. 6. In that position, water isstill retained between vanes 5 and 6 but can begin to flow out of thewheel section defined between vanes 6 and 7. Water continues to flowinto the section between vanes 5, 6 and 7 until the vane 6 passes theedge of the baffle 13 which is at the same vertical height as the axisof the shaft 1. Water then flows into the section between vanes 5 and12. When the wheel has turned through almost 360° it will assume theposition the position shown in FIG. 7. Water flows from the mutuallyisolated sections of the wheel which are in communication with theopening shown in FIG. 2 such that in the position of the wheel shown inFIG. 7 substantially all of the water has been discharged from thesection defined between vanes 5 and 12. As soon as the radially outeredge of the vane 6 becomes immersed in the water below water level 26the cycle is repeated.

[0031] Subject to any minor leakage, all of the water which isdischarged through the drain has had to pass through the screen 19. Anysolids retained by the screen are washed from the outer surface of thescreen as a result of the relatively rapid motion of the screen relativeto the water within the chamber. As soon as the water level subsides toa level below the edge of the baffle 13 which is at the same verticalheight as the rotation axis of the wheel no further water can enter thewheel and therefore it comes to halt.

[0032] In the embodiment of the invention illustrated in FIG. 1 to 7,only one end of the wheel opens into a drain opening. A double-endedembodiment of the invention is possible however as illustrated in FIG.8. The same reference numerals are used in FIG. 8 as are used for likecomponents of the embodiment of FIGS. 1 to 7. The embodiment illustratedin FIG. 8 comprises a single screen 19 but supports two separate baffles13, each baffle 13 being supported by but not rotating with the shaft 1.The baffles 13 thus divide the assembly of FIG. 8 into two sections, onecommunicating with an opening in wall 3 and the other communicating withan opening in wall 4.

[0033] In the embodiments of the invention illustrated in FIGS. 1 and 8the screen 19 is shown as defining an annular gap between itself and theplate or plates 14. Either this gap must be small to prevent significantleakage between the screen 19 and plate 14, or the gap must be closed bya seal. FIG. 9 illustrates one possible sealing arrangement.

[0034] Referring to FIG. 9, the baffle 13 is shown extending from plate14. The screen 19 rotates outside the baffle 13. The end of the screen19 adjacent the plate 14 is strengthened by an annular ring 28 which ispositioned at a distance of for example 12 mm from the end of the screen19, the end of the screen 19 being spaced from the plate by a gap thedimension of which is indicted by arrow 29. The gap is closed by apolymeric seal 30 which is fitted onto the end of the screen 19 anddefines a flexible lip 31 which runs against the plate 14. This preventsany significant leakage between the end of the screen 19 and the plate14.

[0035] Embodiments of the invention could be envisaged in which, ratherthan interposing a baffle between a rotating screen and a rotating vaneassembly, the baffle is located outside the screen. For example, abaffle extending from an upper edge vertically above the wheel shaft toa lower edge vertically below the wheel shaft would ensure that waterwould only enter sections of the wheel located on one side of a verticalplane through the shaft axis. Solid material retained on the outersurface of the screen could in such an embodiment be swept off thatouter surface by for example brushes extending radially inwards from theupper and lower edges of the baffle. As with the embodiments of FIGS. 1to 7 and FIG. 8, the baffle would still ensure that water would enterthe wheel in a manner in which would unbalance the wheel.

[0036] In the embodiment of FIGS. 1 to 7, the baffle extends through270° around the wheel axis and the plate 16 retains water within thewheel sections between the remaining 90° of the circumference of thewheel. It will be appreciated that the baffle could extend around theshaft through an angle of more or less 270°, there being a trade off asbetween the maximum surface area of the screen which can exposed to thewater flow (90° in the case of the embodiment of FIGS. 1 to 7), the rateat which water can be discharged into the drain or drains, and themagnitude of the torque applied to the wheel as a result of theimbalance caused by the different weights of water retained by differentsections of the wheel. The angular extent of the baffle and the angularextent of the plate 16 may also be adjusted as appropriate to suitparticular applications.

[0037] In the illustrated embodiment of the invention, the vanes extendradially from the wheel shaft. Other configurations are possible. Forexample the vanes may be swept back in the direction of rotation of thewheel to smooth the torque applied to the wheel. A swept back vanearrangement is described in the prior art assembly described in theabove mentioned patent specification WO-A-96-27422.

[0038] Although in the described embodiments of the invention thefiltering apparatus is mounted on a shaft extending between two opposedwalls of a chamber, other arrangements are possible. For example, theapparatus may be mounted over an opening in one wall of the chamber, theapparatus projecting from that wall in the manner of cantilever.

1. A liquid filtering apparatus for mounting in a housing defining aninlet and a drain, the liquid filtering apparatus being positioned inuse to filter liquid flowing from the inlet to the drain, the apparatuscomprising a permeable screen rotatable about a substantially horizontalaxis and forming a barrier between the inlet and the drain, a rotatablewheel disposed within the screen and coupled to the screen so thatrotation of the wheel causes rotation of the screen, the wheel definingvanes extending towards the screen to divide a space around which thescreen is arranged into sections which are substantially isolated fromeach other except via the drain, and a stationary baffle arrangedadjacent a portion of the screen to prevent liquid from flowing into thewheel through that portion of the screen, the baffle being positionedsuch that water flows more readily into sections of the wheel on oneside of a vertical plane through the rotation axis than the othersections, whereby the wheel is unbalanced by water retained in sectionsof the wheel so as to cause the wheel to rotate.
 2. An apparatusaccording to claim 1, wherein the housing is formed so as to obstructcommunication between the drain and upper sections of the wheel, intowhich water can flow readily.
 3. An apparatus according to claim 2,wherein the baffle is disposed between the screen and wheel.
 4. Anapparatus according to claim 3, wherein the baffle extends around alower portion and one side of the wheel.
 5. An apparatus according toclaim 4, wherein the baffle extends around more than 180° relative tothe rotational axis, one edge of the baffle being located above therotation axis and the other edge being located to one side of therotation axis.
 6. An apparatus according to claim 5, wherein the baffleextends from a point vertically above the axis to a point horizontallyspaced from the axis.
 7. An apparatus according to claim 1, wherein thevanes extend radially from a shaft, which defines the rotational axis ofthe wheel.
 8. An apparatus according to claim 1, wherein the vanes areswept back relative to the direction of the rotation of the wheel.
 9. Anapparatus according to claim 1, wherein the shaft extends betweenbearings mounted on opposite walls of a chamber.
 10. An apparatusaccording to claim 9, wherein drains are formed in both walls of thechamber.
 11. An apparatus according to claim 1, wherein the apparatus ismounted in the manner of a cantilever from one wall of a chamber. 12.(Cancelled).